Low power factor despite an APFC bank may be caused by unavailable capacitor steps, insufficient kVAR, incorrect CT or voltage reference, changes in load or harmonic distortion. Compare the meter reading, APFC status and alarms before changing settings or installing more capacitors.
What the symptoms may mean
Use these observations to organize the case. They do not confirm a fault by themselves.
| Observation | Possible area | Useful records |
|---|---|---|
| APFC shows all steps ON yet target is missed | Insufficient effective kVAR or failed stages | Controller alarm and step-status log |
| Bank shows demand but steps do not connect | Protection, stage switching or controller issue | Trip indication and stage event log |
| Controller PF differs from main meter | Measurement location or configuration difference | Meter location, CT data and meter parameters |
| Displacement PF looks good, true PF remains low | Distortion from nonlinear loads may contribute | Power quality measurements and THD records |
Understanding the possible causes
Check which power factor is measured
True power factor and displacement power factor are not always the same when harmonic distortion is present. Adding more capacitors does not automatically solve a distortion-related issue and can introduce resonance risks.
Look at the working capacitor stages
A bank can be installed but partly unavailable because of failed steps, protection trips or switching issues. Existing controller alarms, stage status and maintenance records provide useful evidence.
Review CT and sensing configuration
A regulator depends on the correct current-transformer signal and voltage reference. Wrong configuration or a mismatch with the metering point can produce misleading compensation behaviour. Corrections must be designed and made by qualified personnel.
Avoid arbitrary kVAR additions
More capacitors are not a safe universal fix. The load profile, measured kW and kVAR, harmonic content, system impedance and equipment ratings must be reviewed before changes to the compensation design.
Questions to narrow the problem
Start with existing records. Testing and physical inspection require authorization and approved electrical safety procedures.
- Is the reported PF true PF, displacement PF or billing PF?
- What are the recorded APFC controller alarms and active stages?
- Are the main-meter and controller CT locations and ratios documented?
- Did a new UPS, VFD or another nonlinear load start operating?
- What are the measured kW, kVAR and harmonic levels at representative loads?
Next decision
Collect meter records, APFC stage status and representative power-quality results. Arrange an engineering review before changing CT wiring, regulator settings or capacitor-bank size.
Common questions
Why is the APFC controller showing good PF but the bill is poor?
The measurement point, billing period, meter configuration, load variations and true versus displacement PF may differ.
Should we add more capacitors when PF is low?
Not automatically. Confirm usable kVAR, controller inputs and power quality first. Extra compensation may cause problems.
Technical references
References support general fault principles. The applicable manufacturer manual and site procedures take precedence.
- Schneider Electric: PFC controller alarm causes
- Schneider Electric: true and displacement power factor
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